The purposes of the investigation are to study the mechanism of action of the IUD and the prolonged effect of the device on the uterus. A portion of our effort will be to determine the effect of exogenous neutrophils on the in vitro development of blastocysts. Because in hamsters bearing an IUD the ipsilateral ovary is altered, the cellular and subcellular changes of the corpora leutea will be studied. Our data indicate that the IUD alters the response of the uterus to the ovarian hormones. To further substantiate this phenomenon the synthesis of DNA, RNA and SMP will be investigated in IUD bearing horns. BIBLIOGRAPHIC REFERENCES: Krueger, Wayne A., Walter J. Bo and Phillip C. Hoopes 1975 (Dec.) A circadian rhythm of mitotic activity in the uterine luminal epithelium of the rat: Effect of Estrogen. Anat. Rec. 183 : 563-566. Bo, Walter J., Wayne A. Krueger and Benjamin Garrison 1975 (July) Influence of exogenous neutrophils on implantation. Abstract of paper presented at the annual meeting of Society for the Study of Reproduction, July 22-25, Fort Collins, Colorado.